The field of art to which this invention is directed is stable aqueous dispersions of acrylic polymers.
Acrylic ester resin emulsions are well known, having been made commercially for at least 30 years. Such emulsions are made by polymerizing acrylic ester monomer in water using nonionic and anionc surfactants as emulsifiers. Emulsions of this type have been used to manufacture various types of coatings, e.g., exterior and interior house paints. Such emulsions have found limited utility in industrial applications due to the lack of resistance properties, e.g., water resistance, which industrial coatings require.
As described in U.S. Pat. No. 4,177,177, polymer emulsions have been made by the emulsion polymerization of monomers, referred to hereinabove; by the direct emulsification of an organic solvent solution of the polymer in water using an oil-in-water type emulsifier; by the inversion emulsification of an organic solvent polymer solution by adding water to the polymer solution using an oil-in-water emulsifier which can act also as a water-in-oil emulsifier; by emulsification by neutralization wherein acid groups in the polymer are neutralized with a base, e.g., an amine, and the salted polymer is emulsified in water.
In addition to the conventional nonionic and anionic surfactants, various kinds of compounds have been used as dispersants in forming aqueous dispersions of various polymers. One particularly useful dispersant for epoxide resins is described in French Patent No. 2,319,417 and U.S. Pat. No. 4,315,044. This dispersant is the diglycidyl ether of polyoxyalkylene glycols, made from the reaction of epichlorohydrin and the glycol.
In U.S. Pat. No. 3,305,601, organic solvent solutions of acrylic resins containing carboxylic acid functionality are blended with epoxy resins and are cured to form tough, thermoset coatings.
Due to environmental concerns, there is an ongoing effort to decrease or eliminate the use of organic solvents in protective and ornamental coatings and to formulate coatings in aqueous systems which have properties equal to or better than the organic solvent systems.